Direct current motor using magnets with extensions

ABSTRACT

A direct current motor is comprised of an armature, magnets arranged to face each other through the armature, a commutator and brushes. The armature has a core and a plurality of coils wound on the core. Each magnet has a main part and an extension extending form the main part. The main part has an angular interval which corresponds to an interval of winding each coil, so that the extension is positioned outside the coil in the circumferential direction. During the commutation period of the coil, that is, during shorting of the coil by the brush, the amount of magnetic flux passing through the coil is changed by the extension of the magnet. Thus, an induction voltage is generated in the coil to counteract to a reactance voltage of the coil.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a division of application Ser. No.09/536,401, filed on Mar. 28, 2000, now U.S. Pat. No. 6,342,744 entitledDIRECT CURRENT MOTOR USING MAGNETS WITH EXTENSIONS and is related to andincorporates herein by reference Japanese Patent Applications No.11-142042 filed on May 21, 1999, No. 11-203769 filed on Jul. 16, 1999and No. 11-270566 filed on Sep. 24, 1999.

BACKGROUND OF THE INVENTION

The present invention relates to direct current motors having permanentmagnets.

A conventional direct current (d.c.) motor 20 is comprised of permanentmagnets 21 and 22, an armature 23, a commutator 24, brushes 25 and thelike as shown in FIGS. 13A to 13C. In this motor, the armature 23rotates as shown in the order of FIGS. 13A, 13B and 13C, when directcurrent power is supplied thereto.

Specifically, the armature 23 has an armature core 26 and armature coils27. A plurality of teeth 26 a is formed on the core 26. Each coil 27 iswound around five teeth 26 a, although only one is shown in the figures.The coils 27 are wound in a distributed winding form.

The commutator 24 has a plurality of segments 24 a on which the brushes25 slide, so that the direct current flows from the brushes 25 to thecoils 27 through the segments 24 a of a commutator. Thus, the armature23 rotates in the clockwise direction (arrow X) in the figures, as thedirection of current flowing in the coils 27 is reversed.

The current supplied to the coil 27 from the brush 25 is changed asshown in FIGS. 14A to 14C. It is assumed that the current I flows fromright to left as shown in FIG. 14A, and that the commutator 24 moves tothe right as shown in FIG. 14B relative to the brush 15 as the armature23 rotates. The brush 25 bridges two adjacent segments 24 a to supplythe coil 27 with shorting current i. The current I flows from the leftto the right in the coil 27 as shown in FIG. 14C, as the armature 23rotates further. That is, the direction of the current I flowing in thecoil 27 is reversed, when the armature 23 rotates as shown in the orderof FIGS. 14A, 14B and 14C. In this instance, the current which changesby 2I from +I to −I is supplied from the brush 25.

FIGS. 14A to 14C correspond to FIGS. 13A to 13C. When the armature 23rotates as shown in the order of FIGS. 13A, 13B and 13C, the directionof current I in the coil is reversed. The direction of the magneticfield in the core 26 wound with the core coil 27 is reversed. Therotating force is generated to rotate the armature 23 by theelectromagnetic force of the coils 27 and the magnetic force of themagnets 21 and 22.

The reversion of current flowing in the coil 27 during the period ofshorting by the brush 25 is defined as commutation. This relation isexpressed in the following commutation equation.

L(di/dt)+e+Rci+R2(I+i)−R1(I−i)=0

In the above equation, L(di/dt) is a reactance voltage generated by aninductance of the coil 27 shorted by the brush 25, and e is an inductionvoltage generated in the coil 27 when the armature 23 rotates. Rc is aresistance of the coil 27 shorted by the brush 25. R1 and R2 are contactresistances between the brush 25 and the commutator 24. I is a currentsupplied form the brush 25, and i is a shorting current of the coil 27shorted by the brush 25.

The shorting current i changes linearly as shown by the dotted line inFIG. 15, as long as the reactance voltage L(di/dt) of the coil 27 andthe induction voltage e is negligible during the commutation period. Inthis instance, the commutation is effected linearly and most favorable.

However, the reactance voltage and the induction voltage are generatedin the coil 27 in fact. The shorting current i therefore flows with adelay in time relative to the linear commutation characteristics asshown by the solid line in FIG. 15, resulting in an insufficientcommutation. This insufficient commutation causes spark discharges atthe rear end of the brush 25, when the commutation terminates. The sparkdischarges causes noise and brush wear.

It is proposed to counter this problem, that is, improve the commutationoperation by moving the brush in the counter-clockwise direction in FIG.13. The brush is moved to reduce the influence of the induction voltagee. Specifically, the induction voltage e is generated as acounter-electromotive force in the coil 27 by changes in the magneticflux amount Φ passing through the coil 27. This voltage e is expressedas follows.

e=−dΦ/dt

That is, the induction voltage e is generated in proportion to the speedof reduction in the magnetic flux amount Φ passing through the coil 27.

The induction voltage e is shown in FIG. 16.

Specifically, FIG. 16 shows changes in the magnetic flux amount Φpassing through the coil 27 and hence passing through the core 26 (fiveteeth 26 a) around which the coil 27 is wound, and the induction voltagee generated in the coil 27 in response to the change in the magneticflux amount Φ. In FIG. 16, the magnetic flux amount Φ and the inductionvoltage e are shown with respect to a reference position (0°) whichcorresponds to FIG. 13B. That is, the reference position is defined asthe position where the center of the core 26 (five teeth 26 a) woundwith the coil 27 coincides with the center of the magnet 21 or 22.

When no current flows in the coil 27, only the magnetic flux of thepermanent magnets 21 and 22 passes through the coil 27. In thisinstance, the magnetic flux amount Φ is maximal when the rotationposition of the armature 23 is at the reference position (FIG. 13B) asshown by (A) in FIG. 16.

When the current flows in the coil 27, however, it generates themagnetic force which influence the magnetic flux of the magnets 21 and22. As a result, the magnetic flux amount Φ of the coil 27 changes withthe rotation position of the armature 23 as shown by (B) in FIG. 16,because the current is reversed during the commutation period, that is,when the armature 23 rotates as shown in the order of FIGS. 13A, 13B and13C. That is, the magnetic flux amount Φ changes from positive tonegative, when the armature 23 passes through the reference position. Asa result, the magnetic flux amount Φ which actually passes through thecoil 27 changes as shown by (C) in FIG. 16. This amount is a sum of theflux amounts indicated by (A) and (B). Thus, the actual magnetic fluxamount Φ becomes maximum before the armature 23 rotates to the referenceposition. As a result, the induction voltage e of the coil 27 changesfrom negative to positive when the total magnetic flux amount becomesthe maximum. For this reason, the induction voltage e is generated in amanner to delay the commutation and delay the reversion of the shortingcurrent i, causing the insufficient commutation.

Therefore, the influence of the induction voltage e in the coil 27 isminimized by moving the position of the brush 25 in the directionopposite the rotation of the armature 23, that is, in thecounter-clockwise direction in FIG. 13. In practice, the position of thebrush 25 is determined based on not only the induction voltage but alsothe reactance voltage.

It is however difficult to maintain good commutation operation, becausethe current flowing in the coil 27 and the rotation speed of the motorchange from time to time. For instance, in the case of a blower motorused for an automotive air conditioner unit, the position where thetotal magnetic flux amount Φ attains the maximum moves to a position(negative side in FIG. 16) opposite the rotation direction at high loadand high rotation speed conditions because more current is supplied. Theinduction voltage e caused by the total magnetic flux amount Φ alsoincreases as the rotation speed increases. Further, the reactancevoltage also increases as the current in the coil 27 increases. Thus,the brush need be moved more for good commutation operation. In the caseof low load and low speed conditions, on the contrary, the brush need bemoved less for good commutation operation. It is thus required to movethe brush position from time to time.

SUMMARY OF THE INVENTION

The present invention therefore has an object to provide a directcurrent motor capable of attaining good commutation operationirrespective of loads.

According to the present invention, a direct current motor is comprisedof an armature having a core and coils wound on the core, magnetsarranged to face each other through the armature, a commutatoroperatively connected to the coils, and a brush for shorting each coilduring a commutation period to reverse a direction of current in thecoil. Each magnet has an extension at a circumferential end thereof togenerate in the coil an induction voltage which counteracts to thereactance voltage. A commutation characteristics is improved to besufficiently linearized. Preferably, the magnet has, at the extension, avarying thickness or magnetic pole orientation strength different fromthat of its main part. A visible member is provided on the axial end ofthe magnet.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description made withreference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic sectional view showing a direct current motoraccording to a first embodiment of the present invention;

FIG. 2 is a schematic diagram showing a relation between a magnet and anarmature in the first embodiment;

FIG. 3 is a graph showing magnetic flux amount and induction voltagerelative to armature rotation positions in the first embodiment;

FIG. 4 is a schematic diagram showing a relation between the magnet andthe armature in a second embodiment of the present invention;

FIG. 5 is a graph showing magnetic flux amount and induction voltagerelative to armature rotation positions in the second embodiment;

FIG. 6 is a graph showing commutation characteristics;

FIG. 7 is a schematic diagram showing a relation between the magnet andthe armature in a third embodiment of the present invention;

FIG. 8 is a schematic diagram showing a relation between the magnet andthe armature in a fourth embodiment of the present invention;

FIG. 9 is a schematic view showing the magnet used in a fifth embodimentof the present invention;

FIG. 10 is a schematic view showing the magnet used in a sixthembodiment of the present invention;

FIG. 11 is a perspective view showing the magnet used in a seventhembodiment of the present invention;

FIG. 12 is a perspective view showing the magnet used in an eighthembodiment of the present invention;

FIGS. 13A to 13C are schematic sectional views showing a conventionaldirect current motor;

FIGS. 14A to 14C are schematic diagrams showing commutation operation ofthe conventional motor;

FIG. 15 is a graph showing commutation characteristics of theconventional motor;

FIG. 16 is a graph showing magnetic flux amount and induction voltagerelative to armature rotation positions in the conventional motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described in detail with reference tovarious embodiments in which a direct current motor is designed as ablower motor for an automotive air conditioner unit. In the airconditioner unit, the current supplied to the motor is variablydetermined by a manual switch. Specifically, 18 amperes current and 4amperes current are supplied to the motor when the manual switch ismanipulated to a HI-position (high output) and LO-position (low output),respectively. The current determines the rotation speed of the motor andhence the amount of air supplied into the air conditioner unit.

(First Embodiment)

Referring first to FIG. 1, a blower motor 1 is comprised of magnets 2and 3, an armature 4, a commutator 5, brushes 6 and the like. The motor1 is a two-pole direct motor. The magnets 2 and 3 which provide N-poleand S-pole are arranged around the armature 4 to face each other in ahousing 7. The armature 4 has an armature core 8 and armature coils 9wound around the core 8. The armature 4 rotates when the coils 9 aresupplied with direct current. The core 8 is formed with a plurality of(twelve) teeth 8 a. Each tooth 8 a is spaced apart 30° in thecircumferential direction from adjacent teeth. Although only one coil isshown in the figure, each coil 5 is wound on separate five of teeth 8 ain the distributed winding form.

The commutator 5 is disposed at one axial side end of the core 8 and iscomprised of a plurality of segments (commutator pieces) 5 a. Thebrushes 6 are biased to slidably contact the commutator 5. The directcurrent is supplied from a direct current power source to flow from thebrush 6 to the coil 9 through the segments 5 a of the commutator 5.Thus, the armature 4 rotates in the clockwise direction (arrow X) in thefigure, as the direction of current flowing in the coils 9 is reversed.In this embodiment, the direction of the current is reversed every 30°rotation of the armature 4 relative to the brush 6, because each segment5 a is provided every 30° in the circumferential direction. That is, thecommutation of coils is effected every 30° rotation of the armature 4.

The magnets 2 and 3 have main magnetic pole parts 2 a and 3 a andextensions 2 b and 3 b, respectively. The main parts 2 a and 3 acorrespond to the magnets 21 and 22 of the conventional motor (FIG. 13),respectively. The extensions 2 b and 3 b are provided at forwardpositions in the rotation direction, that is, at positions where eachtooth 8 a passes after passing the main parts 2 a and 2 b, respectively.

In FIG. 2, the magnet 2 is shown as straightened although it is in anarcuate shape. Further, the circumferential width of the magnet 2 isindicated in terms of angle and the core 8 (five teeth 8 a) is shown tohave 150° (30°×5). As understood from FIGS. 1 and 2, each main part 2 a,3 a has a circumferential length which corresponds to the angularinterval (120°) between the centers of the first and fifth teeth of fiveteeth 8 a around which each coil 9 is wound. The center of commutationis defined as the rotation position of the armature 4 where the centerof the main part of each magnet and the center (third teeth) of the fiveteeth 8 a align as shown in FIG. 1. The direction of current of the coil9 shorted by the brushes 6 is reversed at this position.

Each extension 2 b, 3 b is gradually thickened over the 30° angularinterval from the end of the main part 2 a, 3 a in the rotationdirection of the armature 4. It is gradually thinned over the 5° angularinterval from the thickest part in the rotation direction of thearmature 4. This 5° angular interval is not limitative but may be moreor less, as long as the motor 1 produces a maximum performance.

Referring further to FIG. 2, the positional relation between magnet 2and the core 8 (five teeth 8 a) wound with the coil 9 is described withrespect to the commutation period.

The commutation starts when the core 8 rotates to the position, wherethe top end of the core 8 align the thinned part 2 c of the magnet 2 asshown by (a) in the figure. When the core 8 rotates 15° further as shownby (b), the core 8 reaches the center of commutation shown in FIG. 1.The direction of current is reversed at this position. The commutationends, when the core 8 further rotates 15° and reaches the position shownby (c) in FIG. 2. That is, the commutation of coil 9 is effected duringthe angular interval 30° in the order of positions (a), (b) and (c). Theextension 2 b is gradually thickened during this commutation period ofangular interval 30°.

The magnetic flux amount Φ passing through the coil 9 under commutationis shown in FIG. 3. In this figure, the reference position 0° indicatesthe rotation position of the armature 4 shown in FIG. 1 in which thecenter of the core 8 (five teeth 8 a) wound with the coil 9 and thecenter of the main part 2 a, 3 a align. As shown in FIG. 3, the magneticflux amount Φ increases gradually as the armature 4 rotates. The rate ofchange in the magnetic flux amount Φ increases as the rotation speed ofthe armature 4 increases. The magnetic flux amount Φ indicates a sum ofthe magnetic flux generated by the current flowing in the coil 9 and themagnetic flux amount generated by the magnets 2 and 3. The dotted linein FIG. 3 shows the magnetic flux amount generated in the conventionalmotor and shown by (C) in FIG. 16.

Further, as shown in FIG. 3, the induction voltage e generated in thecoil 9 is small during an initial period of commutation and graduallyincreases in the negative side as the armature 4 rotates. This inductionvoltage e counteracts to the reactance voltage and improves theinsufficient commutation shown in FIG. 15. That is, the commutationcharacteristics is linearized as shown by the dotted line in FIG. 15 bygenerating the induction voltage e which completely corresponds to thereactance voltage. In the case that the load of the motor 1 is changedby the manual switch of the air conditioner, the current supplied to thecoil 9 changes and the reactance voltage responsively increases anddecreases. In this instance, however, the induction voltage e changes tocounteract the reactance voltage in accordance with the motor load.

Specifically, the reactance voltage increases in accordance with thecurrent of the coil 9, when the manual switch is manipulated to theHI-position to increase the current of the coil 9 to 18 amperes. In thisinstance, the motor rotation speed increases and the induction voltage ealso increases. The reactance voltage decreases in accordance with thecurrent of the coil 9, when the manual switch is manipulated to theLO-position to decrease the current to 9 amperes. In this instance, themotor rotation speed decreases and the induction voltage e alsodecreases. Thus, although the reactance voltage changes with the motorload, the induction voltage e also changes to cancel out the reactancevoltage. As a result, good commutation can be effected even when themotor load changes.

As described above, according to the first embodiment, the inductionvoltage is generated counteract the reactance voltage in accordance withthe motor load without moving the brush. Specifically, the commutationcharacteristics is linearized. As a result, the brush sparks can berestricted, resulting in the reduction of noise and brush wear. Thus,good commutation can be maintained irrespective of changes in the motorload. As the motor 1 can be operated stably, the air conditioner unitcan be operated appropriately with the appropriate rotary driving force.As the brush sparks are restricted, special measures for noises causedby the sparks are not necessitated. The commutation performance can beimproved with ease by changing the shape of the magnets 2 and 3.

(Second Embodiment)

In the second embodiment, each magnet 2, 3 shown in FIGS. 1 and 2 arereplaced with a magnet 11 shown in FIG. 4. The magnet 11 is shown asstraightened form in this figure, although it is actually in an arcuateshape.

As shown in FIG. 4, the magnet 11 has a main part 11 a and an extension11 b extended from one end of the main part 11 a in the direction ofrotation of the core 8. The extension 11 b has a circumferential lengthwhich corresponds to an angular interval of 30°. It is gradually thinnedin the direction of rotation of the core 8. The main part 11 has theother end 11 c which is gradually thinned in the direction opposite thedirection of rotation of the core 8. The rate of thinning relative tothe circumferential length is less at the end 11 b than at the extension11 c.

The magnetic flux amount Φ passing through the coil 9 increases as shownin FIG. 5 during the commutation period in which the core 8 rotates inthe order of (a), (b) and (c). The rate of increase in the magnetic fluxamount Φ relative to the rotation of the armature 4 is maximum at theinitial period of commutation, and gradually decreases with the rotationof the armature 4. As a result, the induction voltage e generated in thecoil 9 is maximum in the negative side at the initial period ofcommutation, and reaches 0 at the end of the commutation period aftergradually increasing from the negative maximum. This induction voltage ealso cancels out the reactance voltage. That is, as shown in FIG. 6, thecommutation characteristics is improved as shown by the solid linerelative to the insufficient commutation shown by the one-dot chainline. This characteristics is sufficiently close to the most desiredcommutation characteristics shown by the dotted line.

The above second embodiment also provides the same advantages as thefirst embodiment. Further, the magnet 11 can be produced with easebecause it needs be thinned simply at its circumferential ends.

(Third Embodiment)

In the third embodiment, a magnet 12 arcuate in shape is formed withextensions 12 b and 12 c at both circumferential ends of a main part 12a as shown in FIG. 7. Each extension 12 b, 12 c has a circumferentiallength which corresponds to the angular interval of 30° for commutation.The extension 12 b has the same uniform thickness as the main part 12 a,while the extension 12 c is thinned gradually in the direction oppositethe direction of rotation of the core 8. In this embodiment also, themagnetic flux amount Φ changes in the similar manner as shown in FIG. 5during the commutation period in which the core 8 rotates in the orderof (a), (b) and (c). The reactance voltage is cancelled out by theinduction voltage e generated by changes in the magnetic flux amount Φand the commutation characteristics is improved as shown by the solidline in FIG. 6.

(Fourth Embodiment)

In the fourth embodiment, a magnet 13 arcuate in shape is formed withextensions 13 b and 13 c at both circumferential ends of a main part 13a as shown in FIG. 8. Each extension 13 b, 13 c has a circumferentialwidth which corresponds to the angular interval of 30° for commutation.The extension 13 b is gradually thinned in the direction of rotation ofthe core 8, while the extension 13 c has a uniform thickness less thanthat of the core 8. In this embodiment also, the magnetic flux amount Φchanges in the similar manner as shown in FIG. 5 during the commutationperiod in which the core 8 rotates in the order of (a), (b) and (c). Thereactance voltage is cancelled out by the induction voltage e generatedby changes in the magnetic flux amount Φ, and the commutationcharacteristics is improved as shown by the solid line in FIG. 6.

(Fifth Embodiment)

In the fifth embodiment, a magnet 14 arcuate in shape is formed to havethe same uniform thickness throughout a main part 14 a and an extension14 b as shown in FIG. 9. However, strength of magnetic dipoleorientation in the extension 14 b is differentiated from that in themain part 14 a. That is, the magnet 14 is magnetized to have a strongorientation part S and weak orientation part W. The orientation isstronger in the extension 14 b than in the main part 14 a, therebygenerating the induction voltage e to counteract to the reactancevoltage.

It is also possible to change strength of magnetization of the magnet tohave strong magnetization and weak magnetization.

(Sixth Embodiment)

In the sixth embodiment, a magnet 15 is shaped to have a main part 15 aand an extension 15 b. That is, the extension 15 b is thinned at its endopposite the main part 15 a, and the orientation is strengthened in theextension.

(Seventh Embodiment)

In the case of such a magnet 14 having the uniform thickness as in thefifth embodiment (FIG. 9), it may be difficult to distinguish theextension 14 b from the main part 14 a from its outer configuration. Themagnet 14 is likely to be assembled to the housing 7 in reverse.Further, the cummutation performance cannot be improved, if the magnet14 is displaced from its right position in the assembling process.

Therefore, in the seventh embodiment, a recess or concavity 16 is formedon the arcuate magnet 14 to be visible externally as shown in FIG. 11.It is preferably provided at a position displaced from the central line(circumferential center) L of the magnet within the range of the mainpart 14 a. This recess 16 can be formed in the magnet molding process.It is preferred that the recess 16 is provided on the corner where theaxial side end surface and the planar outer peripheral surface cross, sothat it may be recognized externally even after the assembling process.The recess 16 may be replaced with a protrusion or convexity. The recess16 or protrusion should be sized and positioned not to influence themagnetic flux amount of the magnet 14 nor lessen the mechanicalstrength.

(Eighth Embodiment)

In the eighth embodiment, a colored marking 17 is provided by printingor the like as shown in FIG. 12. The marking 17 is provided on thecircumferential end of the side end surface of the magnet 14.

In the foregoing embodiments, the extensions may be formed intodifferent shapes as long as the commutation characteristics is generallylinearized. For instance, the extensions may be a shape so that thecurrent may change smoothly, that is, the commutation may be effected ina sine-wave characteristics, at the start and end of the commutation.The recess, protrusion and marking may also provided on the magnets usedin the first to fourth embodiments (FIGS. 1 to 8).

Further modifications and alterations are also possible withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A direct current motor comprising: an armaturehaving a core and coils wound on the core; magnets arranged to face eachother through the armature; a commutator operatively connected to thecoils; and a brush disposed in sliding contact with the commutator forshorting each coil during a commutation period to reverse a direction ofcurrent in the coil, wherein each magnet has a main part and anextension part at an end of the main part to generate in the coil aninduction voltage that counteracts a reactance voltage, wherein the mainpart and the extension part have a similar uniform thickness; wherein amagnetization in the extension part at an end side in a rotationdirection of the armature is stronger than that at a boundary partbetween the main part and the extension part, and wherein a magneticdipole orientation in the main part is directed to a rotation axis ofthe armature, a magnetic dipole orientation in the boundary part betweenthe main part and the extension part is directed to a radially outerside from the rotation axis of the armature and a magnetic dipoleorientation in the end side of the extension part is directed to therotation axis of the armature.
 2. The direct current motor of claim 1,wherein each magnets have thinned ends at both terminal ends.
 3. Thedirect current motor of claim 1, wherein the magnet has a visible memberthereon at a location other than a planar surface, which is attached toa housing.
 4. The direct current motor of claim 3, wherein the visiblemember is provided at a position deviated from a center of the magnet ina circumferential direction.
 5. The direct current motor of claim 4,wherein the visible member is provided within a range of the main part.6. The direct current motor of claim 4, wherein the visible member isprovided at one terminal end of the magnet.
 7. The direct current motorof claim 4, wherein the visible member is a recess.
 8. The directcurrent motor of claim 4, wherein the visible member is a coloredmarking.
 9. The direct current motor of claim 1, wherein the extensionpart extends respective angular ranges each of which includes acommutation interval.
 10. The direct current motor of claim 1, whereinthe extension part extends respective angular ranges each of whichcorresponds to an angular interval between two adjacent teeth of thearmature on which the coils are wound.
 11. A direct current motorcomprising: an armature having a core and coils wound on the core;magnets arranged to face each other through the armature; a commutatoroperatively connected to the coils; and a brush disposed in slidingcontact with the commutator for shorting each coil during a commutationperiod to reverse a direction of current in the coil, wherein eachmagnet has a main part and an extension part at an end of the main partto generate in the coil an induction voltage that counteracts areactance voltage, and wherein a magnetization in the extension part atan end side in a rotation direction of the armature is stronger thanthat at a boundary part between the main part and the extension partwherein the magnetic dipole orientations in the main part and in theextension part are respectively and substantially directed toward arotational axis of the armature.
 12. A direct current motor comprising:an armature having a core and coils wound on the core; magnets arrangedto face each other through the armature; a commutator operativelyconnected to the coils; and a brush disposed in sliding contact with thecommutator for shorting each coil during a commutation period to reversea direction of current in the coil, wherein each magnet has a main partand an extension part at an end of the main part to generate in the coilan induction voltage that counteracts a reactance voltage, and wherein amagnetic dipole orientation in the main part is directed to a rotationaxis of the armature, a magnetic dipole orientation in a boundary partbetween the main part and the extension part is directed to a radiallyouter side from the rotation axis of the armature and a magnetic dipoleorientation in an end side of the extension part is directed to therotation axis of the armature.